Exhaust gas aftertreatment device

ABSTRACT

The invention relates to an exhaust gas aftertreatment device ( 1 ) of a motor vehicle, said device having a heater ( 2 ), which includes a plurality of heating elements ( 5, 6, 7 ), and a control unit ( 9 ) associated with the heater ( 2 ), wherein a common first switch ( 10 ) and in each case a second switch ( 32, 33, 34 ) are associated with the heating elements ( 5, 6, 7 ) and said heating elements ( 5, 6, 7 ) are jointly switchable by means of the first switch ( 10 ) and individually switchable by means of the second switches ( 32, 33, 34 ). The invention thereby provides that said first switch ( 10 ) is disposed separately from the control unit ( 9 ) and can be actuated by the same.

This application claims benefit of Serial No. 10 2009 046 769.6, filed 17 Nov. 2009 in Germany and which application is incorporated herein by reference. To the extent appropriate, a claim of priority is made to the above disclosed application.

BACKGROUND

The invention relates to an exhaust gas aftertreatment device of a motor vehicle having a heater, which includes a plurality of heating elements, and a control unit associated with the heater. A common first switch and in each case a second switch are associated with the heating elements and said heating elements can be jointly switched by means of the first switch and individually switched by means of the second switch.

Exhaust gas aftertreatment devices of the type mentioned above are known from prior art. They are frequently used in the commercial vehicle sector. The heater is supplied with current via a main path, which can be switched via the first switch. The individual heating elements of the heater can also be individually switched via the second switch, which in each cased is associated with them. The first switch and the second switches are thereby normally disposed in the control unit associated with the heater. The heater, respectively the heating elements are therefore supplied with current via said control unit as soon as the first switch and the respective second switch are closed. In doing so, the heating elements can only then be switched on by means of the second switches if the first switch is closed. For this reason, the first switch is connected in series with the heater and the second switches are in each case connected in series with the individual heating elements. As a result, the first switch and the second switches are embodied as electrical switches. A method for controlling an electrical heater of a catalytic converter for the exhaust gas purification of an internal combustion engine in a motor vehicle is known from the German patent specification DE 44 22 198 A1. Two batteries are thereby provided; both of which can be connected to the electrical heater. In so doing, provision is made for the batteries to be decoupled from each other before switching on the heater, so that a load is being placed on only one of said batteries while the other battery can continue to supply an electrical system of the vehicle. A disadvantage of the exhaust gas aftertreatment of prior art is that in each case a power loss is incurred at the first switch and the second switches. For this reason, the control unit, in which the switches are normally disposed, must be designed accordingly. A large power loss is incurred particularly at the first switch because the heater and hence all heating elements are supplied with current via said switch.

SUMMARY

In contrast, the exhaust gas aftertreatment device with the features of claim 1 has the advantage that the power loss incurred in the control unit is significantly smaller than that from prior art. The inventive device achieves this objective by the first switch being disposed separately from the control unit and being actuated by the same. Said control unit can in this way be designed with smaller dimensions because a cooling device for said first switch is eliminated. The cooling device is, for example, a passive heat sink and/or an active cooling system, which particularly comprises a fan. Said first switch can furthermore be actuated by said control unit. A cable is especially provided for this purpose between said control unit and said first switch. Said first switch can be advantageously implemented by means of an electronic or mechanical relay. This relay is triggered by said control unit, whereby it is assured that the heater can be quickly switched off should a malfunction of the heater and/or said control unit be detected. It is for this reason advantageous if said first switch is open in an initial position and is first brought into a switching position, in which said first switch is closed, by a corresponding actuation by means of the control unit. As soon as said first switch is no longer actuated by said control unit, it advantageously returns to its initial position whereby the heater is switched off.

Provision is made in a modification to the invention for at least a portion of the second switches to be provided in the control unit or likewise to be disposed separately from said control unit and to be capable of being actuated by the same. Provision can therefore be made for said second switches to be disposed at said control unit while the first switch is arranged separately therefrom. As an alternative, it is possible to also dispose the second switches or at least a portion of the same separately from said control unit and to actuate them via the same. In the case of such an embodiment of the exhaust gas aftertreatment device, the power loss, which is incurred in said control unit, can be further reduced. It is especially possible for a separate current supply to be provided for the control unit; thus enabling control unit and heater to be supplied by power sources which are independent of one another. Because the current flowing through the heater is not conveyed by said control unit, it is possible to design said heater for currents, which could not be realized if the current were directly supplied via said control unit. This also likewise means that said control unit can be constructed even smaller because cables and terminals of said control unit merely have to be matched to reduced currents.

Provision is made in a modification to the invention for the first switch to be provided between the heating elements and a positive pole of a direct current source. Said first switch is therefore embodied as a so-called high-side switch. The heater, respectively the heating elements, can thus be separated from the positive pole via said first switch. This is particularly advantageous if a short circuit is present in said heater because a stress on the direct current source as a result of the short circuit can be avoided.

Provision is made in a modification to the invention for the second switches to be provided between the heating elements and a negative pole or between the first switch and the heating elements. If the former is the case, the second switches are configured as low-side switches. This has the advantage that a simpler actuation of the switch is possible, for example, when using an electronic switch (transistor or the like). If on the other hand the second switches are disposed between the first switch and the heating elements, said second switches also form high-side switches and are therefore able to directly separate the heating elements from the positive pole of the direct current source.

A modification to the invention provides that the first switch and/or the second switches are relays or electronic assemblies. The switches can basically be arbitrarily embodied. It is, however, advantageous if said first and/or said second switches are embodied in particular as mechanical relays or as electronic assemblies. The electronic assembly has, for example, a transistor or a similar switching unit, which can be actuated by the control unit.

A modification to the invention provides for a diagnostic device to be associated with the first and/or at least a second portion of the second switches and/or at least a portion of the heating elements. A defect in the switches and/or the heating elements can, for example, be detected by means of the diagnostic device. If a defect is present, suitable measures can then be taken. The first switch, for example, is opened so that the heater is turned off. Provision can be made, however for said diagnostic device to detect a switching state of the first and/or the second switch and to make this information available to the control unit. In order to meet this objective, said diagnostic device is connected to said control unit by means of circuitry.

A modification to the invention provides that the diagnostic device is connected to the control unit or is formed from the same. In the former case, said diagnostic device is, for example, disposed in the region of the first switch, the second switch and/or the heater. In so doing, it is connected to said control unit in order to provide the same with feedback about the operating status of the exhaust gas aftertreatment device, for example, the operating status of switches, the heater and/or individual heating elements. Said diagnostic device can, however, also be formed from said control unit, respectively be an integral part thereof. In this case, a sensor, the sensor values of which are evaluated by said diagnostic device, can in each case be associated with the component to be diagnosed, hence the first switch, the second switches, the heater and/or the heating elements.

A modification to the invention provides for the control unit to be designed in such a way that the first switch is actuated to turn off the heating elements when an error occurs. The occurrence of the error is, for example, detected by the diagnostic device. In order to avoid damage to the exhaust gas aftertreatment device, the heater is turned off by the heating elements being deactivated. For this purpose, the first switch is opened by the control unit by appropriate actuation. Said first switch is configured for the purpose of turning off the heating elements as soon as an actuation of said switch does not occur.

A modification to the invention provides that the control unit is connected to the same power source as the heater or to a separate power source. As previously mentioned, the heater is connected to the same power source as the control unit if only the first switch is disposed separately from said control unit. If the second switches are additionally provided outside of said control unit, said control unit can then be connected to a separate power source. In this way, said control unit can, for example, be operated with a different supply voltage than the heater.

Provision is made in a modification to the invention for an overvoltage protection device to be provided between the power source and the control unit and/or the heating elements. In order to protect said control unit, respectively said heating elements, from too high a voltage, the overvoltage protection device is provided in the exhaust gas aftertreatment device. Said overvoltage protection device can, for example, be provided by circuitry means between the positive pole of the dc current source and the first switch. Said overvoltage protection device can be a voltage filter or alternatively interrupting means, which separate the power source from said control unit, respectively the heating elements, as soon as being subjected to an overvoltage. Said overvoltage is thereby a voltage, which is greater than a certain maximum voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is subsequently explained in detail with the aid of the exemplary embodiments depicted in the drawing. No limitation to the invention results from the explanation of said embodiments. The following are shown:

FIG. 1 is a region of a first embodiment of an exhaust gas aftertreatment device, and

FIG. 2 is a region of a second embodiment of the exhaust gas aftertreatment device.

DETAILED DESCRIPTION

FIG. 1 shows a region of an exhaust gas aftertreatment device 1 of an unspecified motor vehicle. The exhaust gas aftertreatment device 1 comprises, for example, a heater 2 having five heating elements 3, 4, 5, 6 and 7 and a switching valve 8. The heating elements 3, 4, 5, 6, and 7 are, for example, embodied as heating wires, filaments or the like, while an unspecified coolant circuit for removing heat from the heating elements 3 to 7 can be released, respectively interrupted, by the switching valve 8. The heater 2 can be associated with an SCR system, wherein it serves to heat at least one pipeline, through which an operating means (for example a water-urea solution) is supplied to a catalytic converter (unspecified). A water-urea solution that is typically used freezes at approximately −10EC so that at low outside temperatures a heating of the pipeline by means of the heater 2 is necessary to thaw the water-urea solution, respectively maintain the liquid state of said solution. The heat of at least one of the heating elements 3 to 7 is supplied to the pipeline via the coolant circuit. In order to meet this objective, the heater 2 is activated by a control unit 9 assigned thereto.

Furthermore, a first switch 10 is provided, which can be actuated by the control unit 9 via an actuator 11. For this purpose, the actuator 11 is connected to said control unit 9 via cables 12 and 13. The cable 12 is connected to cables 14 and 15, which can be connected to a positive pole 17 of a direct current source, which is not specified here. The switch 16 serves thereby as a so-called high-side switch for said actuator 11, the heating element 3 as well as the switching valve 8, which are connected to the switch 16 via the cables 12, and 14. The heating element 4 can be connected to the positive pole 17 via an additional switch 18 and a cable 19. Also the switch 18 is accordingly embodied as a high-side switch. Said actuator 11 can be connected to a negative pole 21 of the direct current source via the cable 13 and a switch 20. This is likewise true for the heating element 3 via a switch 22 and a cable 23 and for the switching valve 8 via a switch 24 and a cable 25.

The actuator 11 can only then be activated if the switch 16 as well as the switch 20 is closed so that said actuator 11 is connected to the positive pole 17 as well as to the negative pole 21. This also applies analogously to the heating element 3 and the switching valve 8; and in so doing the switch 22, respectively the switch 24, has to be closed. The heating element 4 can be connected to the positive pole 17 as well as to the negative pole 21 and thereby be activated by closing both the switch 18 and a switch 26, which is connected to the heating element 4 via a cable 27.

The first switch 10, which can be actuated by means of the actuator 11, serves as a high-side switch for the heating elements 5, 6 and 7. These can consequently be connected to the positive pole 17 by closing said switch 10, which is provided via actuation of the actuator 11 by the control unit 9. For this purpose, the first switch 10 is connected to the heating elements 5, 6 and 7 via a common cable 28. On the side of said heating elements 5, 6 and 7 which faces away from said first switch 10, said heating elements 5, 6 and 7 are connected to the second switches 32, 33 and 34 via cables 29, 30 and 31. Said second switches 32, 33, and 34 serve as low-side switches for said heating elements 5, 6 and 7; thus they can establish a connection to the negative pole 21.

It can be seen that the heating elements 5, 6 and 7 are jointly switchable via the first switch 10 and are individually switchable via the second switches 32, 33, and 34. In this exemplary embodiment, said first switch 10 is thereby disposed outside of the control unit 9, respectively separated from the same, can, however, still be actuated by said control unit 9. The actuator 11, as already described, is provided for this purpose. The second switches 32, 33, and 34 are likewise actuated by said control unit 9; however—in contrast to said first switch 10—are disposed therein. It is then obvious that said first switch 10 is provided between the heating elements 5, 6 and 7 and the positive pole 17 and said second switches 32, 33, 34 are provided between said heating elements 5, 6 and 7 and the negative pole 21. Said first switch 10 is thereby embodied as a mechanical relay, which is actuated, respectively switched, by means of the actuator 11. As a result, said actuator 11 can, for example, be a magnetic actuator. Said second switches 32, 33 and 34 are preferably embodied as electronic components, for example, as transistors (or MOSFET), respectively power transistors. By means of the external disposal of said first switch 10, the power loss incurred in said control unit 9 can be significantly reduced. In the case depicted here, said control unit 9 and the heater 2 are connected to the same power supply.

FIG. 2 shows a further embodiment of the exhaust gas aftertreatment device 1, wherein again merely a cut-out is depicted. Only the heating elements 5, 6 and 7 are depicted for this embodiment, which are jointly switchable by means of the first switch 10 and individually, respectively separately, switchable by means of the second switches 32, 33 and 34. Said first switch 10 is in turn actuated by the control unit 9 via the actuator 11. For that purpose, said actuator 11 is connected to said control unit 9 via the cables 12 and 13. Said cables 12 and 13 can be connected to a positive pole 35 via the switch 16 and to a negative pole 36 via the switch 20 of a separate power source not depicted here, in particular a direct current source. The power supply of the heating elements 5, 6 and 7 is on the other hand still implemented via the positive pole 17 and the negative pole 21. For that purpose, said first switch 10 as well as said second switches 32, 33, and 34 is disposed between said heating elements 5, 6 and 7 and the positive pole 17. Said first switch 10 as well as said second switches 32, 33, 34 are accordingly embodied as high-side switches for said heating elements 5, 6 and 7. Said heating elements 5, 6 and 7 are connected directly to the negative pole 21 of the direct current source on the side facing away from said second switches 32, 33, and 34.

The second switches 32, 33, and 34 are connected to the control unit 9 via the cables 37, 38 and 39 and can be connected here to the negative pole 36 via the switches 40, 41 and 42. Said second switches 32, 33 and 34 are thereby embodied, for example, as transistors; thus enabling them to become electrically conductive when the first switch 10 is closed and when switches 40, 41 and 42 are in each case closed and as a result switch on the heating elements 5, 6 and 7. In this embodiment, the first switch 10 as well as the second switches 32, 33 and 34 are disposed outside of, respectively separately from, the control unit and can be actuated by the same. That means that the power loss incurred in the control unit 9 can be further reduced in comparison to the embodiment of FIG. 1. Furthermore, separate power sources for said control unit 9 and the heater 2 can be advantageously provided.

In the embodiment depicted, the heater 2 is connected to the direct current source and the control unit 9 to the separate direct current source. Thus, the heating elements 5, 6 and 7 can, for example, be supplied with a higher operating voltage than said control unit 9. In addition, an unspecified protection device can be provided. This is preferably disposed between the positive pole 17 and the first switch 10. The protection device protects said heating elements 5, 6 and 7 from the occurrence of current pulses which are too high or from overvoltage, respectively voltage pulses, which could lead to damage to said elements. 

1. Exhaust gas aftertreatment device of a motor vehicle, said device having a heater, which includes a plurality of heating elements, and a control unit associated with the heater, wherein a common first switch and in each case a second switch are associated with the heating elements and said heating elements are jointly switchable by means of the first switch and individually switchable by means of the second switches, wherein said first switch is disposed separately from the control unit and can be actuated by the same.
 2. Exhaust gas aftertreatment device according to claim 1, wherein at least a portion of the second switches is provided in the control unit or is likewise disposed separately from said control unit and can be actuated by the same.
 3. Exhaust gas aftertreatment device according to claim 1, wherein the first switch (10) is provided between the heating elements and a positive pole of a direct current source.
 4. Exhaust gas aftertreatment device according to claim 1, wherein the second switches are provided between the heating elements and a negative pole or between the first switch and said heating elements.
 5. Exhaust gas aftertreatment device according to claim 1, wherein the first switch and/or the second switches are relays or electronic assemblies.
 6. Exhaust gas aftertreatment device according to claim 1, wherein a diagnostic device is associated with the first switch and/or at least a portion of the second switches and/or at least a portion of the heating elements.
 7. Exhaust gas aftertreatment device according to claim 1, wherein the diagnostic device is connected to the control unit or is formed by the same.
 8. Exhaust gas aftertreatment device according to claim 1, wherein the control unit is adapted to actuate the first switch so as to switch off the heating elements in the event that an error occurs.
 9. Exhaust gas aftertreatment device according to claim 1, wherein the control unit is connected to the same power source as the heater or to a separate power source.
 10. Exhaust gas aftertreatment device according to claim 1, wherein an overvoltage protection device is provided between the power source and the control unit and/or the heating elements. 